This invention relates to an apparatus including a regenerative burner for repetitively regenerating a trap element located in the exhaust system of an internal combustion engine.
It has been proposed to purify exhaust gas from an automobile internal combustion engine by employing a trap or particle filter element located in the exhaust system of the engine to collect therein carbon or other particles included in the exhaust gas discharged from the engine. The trap element should be repetitively regenerated each time a regeneration requirement occurs; that is, when the amount of the exhaust particles collected in the trap element reaches a limit value. For this purpose, a regenerative burner is disposed in the exhaust system upstream of the trap element, the regenerative burner including a glow plug operable to ignite and burn an air-fuel mixture supplied into the burner so as to burn the exhaust particles collected in the trap element when a regeneration requirement occurs.
The regenerative burner has a liner closed at its upstream end by an end plate to define therein a combustion chamber opening toward the trap element. The liner formed in its side wall with a number of holes to permit flow of exhaust gas from the engine exhaust conduit to the trap element. The liner contains a cylindrical cup which is secured at its upstream end on the end plate and which extends into the combustion chamber to define an evaporation chamber therein. The cup has a cylindrical side wall formed with a number of flame holes to permit fluid flow from the evaporation chamber into the combustion chamber. The evaporation chamber has a supply of air-fuel mixture through a mixture conduit which has one end terminating in a discharge outlet extending through the end plate into the evaporation chamber. The air-fuel mixture charged in the evaporation chamber is ignited by a glow plug when a regeneration requirement occurs.
A disadvantage with such an apparatus is that under low speed and low load conditions such for example as idle conditions where the temperature of exhaust gas is relatively low and the amount of fuel required for the regenerative burner is relatively great, the fuel fed through the mixture conduit is not heated to a temperature sufficient to be evaporated completely, resulting in degraded combustion in the regenerative burner. This difficulty stems mainly from the conventional design of the regenerative burner wherein the air-fuel mixed fed through the mixture conduit is preheated only by exhaust gases from the engine.
The present invention provides an improved exhaust purification apparatus which can provide improved burner combustion efficiency to improve trap regeneration efficiency and also creates stable flame in the burner to provide uniform trap regeneration over the entire range of engine operating conditions.